There are 2 major causes of ICRS extrusion: (1) su- perficial implantation of a segment and (2) a segment that is placed too close to the incision.

1. Reasons for intrastromal corneal ring segment
explantation
In their recent article, Ferrer et al.1
report that 57 of
250 implanted intrastromal corneal ring segments
(ICRS) had to be explantedda rate of 22.8%. The
main cause of this very high explantation rate was
extrusion (48.3%).
There are 2 major causes of ICRS extrusion: (1) su-
perficial implantation of a segment and (2) a segment
that is placed too close to the incision. As a general
rule, the thickness of the implanted ICRS should not
be more than 50% of the corneal thickness in the ring
track. Moreover, the incision depth should preferen-
tially be set at 80% of the corneal thickness. Deeply
located ICRS produce better results and also leave
a greater amount of corneal stroma between the
ICRS and the corneal epithelium, which could theoreti-
cally protect from extrusion related to progressive
stromal thinning. Only rarely does an extrusion begin
in the middle of the segment or far from the incision.
An ICRS that is placed close to the incision, especially
if implanted superficially, predisposes to adjacent cor-
neal thinning and melting and subsequent extrusion.
As our knowledge about the corneal response to
ICRS implantation has evolved, we now implant
thinner segments to achieve the same or better results
than in the past. One of the most feared complications
of ICRS implantation, ring extrusion, is now less
common because we respect the pachymetry rule.
We do not believe that the inflammatory cells and
cell debris found in cases of extrusion are the cause
but rather the consequence of the extrusion. The pro-
gressive epithelial and stromal thinning can lead to
segment exposure, which in turn can lead to a local in-
flammatory reaction, triggering corneal melting
around the segment, with consequent extrusion.
It would be important to know the device used to
measure the corneal pachymetry in Ferrer et al.’s study
as there are differences among the most commonly
used devices.2,3
The explanted ring thickness and
ring track pachymetry should also be described to
clarify the relationship between ring extrusion and
corneal thickness.
Leonardo Torquetti, MD, PhD
Paulo Ferrara, MD, PhD
Belo Horizonte, Brasil
REFERENCES
1. Ferrer C, Alio JL, Monta~nes AU, Perez-Santonja JJ, Diaz del
Rio MA, Alvarez de Toledo J, Teus MA, Javaloy J. Causes of
intrastromal corneal ring segment explantation: clinicopatho-
logic correlation analysis. J Cataract Refract Surg 2010;
36:970–977
2. Prospero Ponce CM, Rocha KM, Smith SD, Krueger RR. Central
and peripheral corneal thickness measured with optical
coherence tomography, Scheimpflug imaging, and ultrasound
pachymetry in normal, keratoconus-suspect, and post-laser in
situ keratomileusis eyes. J Cataract Refract Surg 2009;
35:1055–1062
3. Bourges J-L, Alfonsi N, Laliberte J-F, Chagnon M, Renard G,
Legeais J-M, Brunette I. Average 3-dimensional models for the
comparison of Orbscan II and Pentacam pachymetry maps in
normal corneas. Ophthalmology 2009; 116:2064–2071.
Available at: http://download.journals.elsevierhealth.com/pdfs/
journals/0161-6420/PIIS0161642009004229.pdf. Accessed July
22, 2010
REPLY: Although the incidence of ICRS explantation
is an interesting question, these data are beyond the
scope of our work. The goal of our study was not to
know the explantation rate but rather to know the
main cause of explantation in the first 9 years of
segment implantation and correlate it with pathologi-
cal findings. Because of the comments of Torquetti and
Ferrara, we would like to emphasize that an explanta-
tion rate of 22.8% in 9 years is not very high if you
consider that this period included all ICRS implanta-
tions performed in our clinic since the first one. This
involved the clinicians’ learning curve, obsolete
implantation techniques, the first ring models, the first
measurement methods, and the lack of a standard
nomogram for the implantations. In addition, we are
a referral center and difficult cases from other centers
are sent to us; this affected the explantation rate.
Nine years is a long period of time and as time passes,
the probability of explantation increases. How many
segments implanted in 2000 remain in the patient?
Regarding the extrusion cases, slightly less than
half the explanted segments were due to extrusion
(48.3%); therefore, approximately 10% of the
segments implanted over 9 years were explanted
because of extrusion. This group includes the seg-
ments that were too close to the incision or positioned
superficially and those that extruded because of
corneal thinning (advanced keratoconus). Table 3 of
our article shows that the time from implantation to
explantation ranged from 0.1 to 82.0 months. It is
normal to assume that a longer implantation-
to-explantation time (years) was caused by stromal
thinning over time and a shorter time was due to in-
correct positioning. In all cases, the pachymetry rules
were respected.
Although we have reread our article twice, we can-
not find any place in which we said the inflammatory
cells were the cause of extrusion. However, there is
a paragraph in the discussion section (page 975) in
which we commented on how the inflammatory
response is triggered in the extrusion process.
Q 2010 ASCRS and ESCRS 0886-3350/$dsee front matter
Published by Elsevier Inc. doi:10.1016/j.jcrs.2010.08.025
2014
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